HISTORY OF FLIGHT—LOENING 349 
cantilever stressed-skin monoplane, but used plywood covering, which 
could not take the weather. 
LANDING GEARS 
In earlier years, landing gears had skids to which wheels were 
added, but the skids were the cause of many wrecks when they broke 
on hard landings. From the very beginning, wheels alone were 
obviously correct. In Europe, Bleriot, and in America, Curtiss, were 
alone in realizing this, and in the case of Curtiss we must recognize 
that the practical three-wheel gear was constantly being demon- 
strated as successful and correct by the early Curtiss planes, but 
practically no one else saw this. Even Curtiss gave it up about 1915. 
The advantage of being able to land and take off in a cross wind was 
lost. And yet some 35 years later the three-wheel gear with level 
fuselage configuration came back into practically worldwide usage. 
Brakes on wheels were suggested at an early date, but the majority 
of the air industry scoffed at the idea because to them it was only 
too obvious that applying the brakes too strongly would turn the 
plane over. Soa few feeble braking features were used on tail skids. 
Then came the question of retractable landing gears. The desirabil- 
ity of these should have been obvious at the earliest date at which we 
reached 100 miles per hour, which was in 1912. But history shows that 
it was the advent of the successful amphibian plane (which had to 
have its landing gear foldable) that taught the lesson that retracting 
a landing gear and housing it were neither too complicated nor too 
heavy. There had been several successful landplanes with folding 
gear, notably the Verville monoplane of 1922. Nevertheless, it was 
some 6 or 8 years before retractable gears came into more general use. 
PROPELLERS 
Variable-pitch propellers were suggested at an early date—a prac- 
tical one by Hamilton in the twenties—but it took 8 or 10 years for 
these to come into wide and general use. Incidentally, even the advent 
of the metal propeller so competently developed by Sylvanus Reed, 
after solving forging difficulties, took far too much time for 
acceptance. 
ENGINE PLACEMENT 
On the early configurations in America, engines were to the side of, 
or behind, the aviator. In the case of the original Wright design, the 
translating of 12 horsepower into effective enough thrust to fly 750 
pounds required the two large geared-down propellers—and, in fact, 
this was one of the secrets of the Wrights’ success. As more powerful 
engines came along, such as Curtiss’s motorcycle engine, the gearing 
down was not needed, but the engines remained behind the pilot. 
